Fig. 4.

A–D. Ca²⁺ waves and contractions. A and C show fields of view (FOV) of chicken EOM preparations. An ST map was constructed by averaging the fluorescence intensities perpendicular to the long axis of adjacent myofibers in the area encompassed by the white dashed rectangle (B and D). A Ca²⁺ initiated in the rightmost myofiber (arrowhead in ST map in B) that caused a contraction after a delay of ~200 ms (blue trace in E). The contraction was more easily measured in the leftmost myofiber as the distance between the two white tracking rectangles in A. Fast Ca²⁺ transients evoked by a train of electrical impulses (C and ST Map in D) did not result in any appreciable distortion of muscle fibers (see E, magenta trace). The distortion due to longitudinal contraction could also be visualized by examining the shape of the Ca²⁺ wave as shown in F. The “bulging” of the myofiber, most likely due to longitudinal compression, was maximal 0.6–0.8 s after elevated Ca²⁺ levels were detected. The diameter of the myofiber made visible by the Ca²⁺ wave was color-coded, such that the normal resting diameter of the myofiber (~10 μm) was colored green and dilated regions were colored red (15–17 μm; see F). In this example, the Ca²⁺ wave propagated from the bottom to the top of the FOV at different speeds (see silhouettes at 0, 2.2 and 4.5 s in F), resulting in an elongation of the “teardrop” shape at higher velocities.